Permanent magnet chuck



Jan. 25, 1966 J. N. ENGELSTED PERMANENT MAGNET CHUCK 3 Sheets-Sheet 1 Filed Aug. 24, 1956 Fig. I

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Jan 25, 1966 J. N. ENGELSTED 3,231,789

PERMANENT MAGNET CHUCK Filed Aug. 24, 1956 3 Sheets-Sheet 5 Fig. 7

0N OFF e4 ee INVENTOR. JOHN N. ENGELSTED ATTORNEYS United States Patent O 3,231,789 PERMANENT MAGNET CHUCK John N. Engelsted, Petersham, Mass., assignor to 0. S.

Walker Company, Inc., Worcester, Mass., a corporation of Massachusetts Filed Aug. 24, 1956, Ser. No. 606,017 7 Claims. (Cl. 317-159) The present invention relates to magnetic work-holding and lifting devices and more particularly to permanent magnet chucks, including permanent magnet lifting devices.

Work-holders or chucks off both the electromagnetic and the permanent magnet type are well known in the art. The permanent magnet chuck possesses the advantage of being entirely self-contained, free of the nuisance and hazard of a power cord. On the other hand, the permanent magnet type presents the problem of affording adequate holding power, yet capable of releasing the work freely when Ithe Work is to be removed or repositioned.

Permanent chucks begain to be practical with the advent of the nickel-cobalt alloys particularly those designated by the term Alnico. Arrangements were devised for reducing the flux `at the top surface when desired, to release the Work.

One of the problems with permanent chucks to date has been to provide, in a practical construction, a working surface wherein numerous poles of opposite polarity are presented, in order that relatively small Work pieces may be held. It has been considered heretofore that the magnet material should best be employed in terms of a relatively few powerful magnets, with the top plate divided into poles in a manner affording a reasonable degree of subdivision consistent with the problem of distributing the flux from the magnets.

More recently, magnet materials offering still further improvement in flux density and coercive force have become available. These materials, in the nature of ceramics, have properties that permit them to be effectively magnetized in a direction across relatively narrow dimensions, so that opposite poles exist on opposite sides of a relatively narrow section. By utilizing such materials in a novel and effective manner, it becomes possible as will hereinafter appear to provide permanent magnet chucks and lifting devices which have powerful holding ability, free release, and a sub-divided work-holding surface presenting numerous pole divisions for holding or lifting small work as well as large.

It is therefore an object of the invention to provide a permanent magnet Work-holding or work-lifting device of novel construction and arrangement Wherei'nthe magnet material may be utilized in a highly effective manner to provide a working surface having numerous pole divisions.

It is likewise `an object of the invention to provide a permanent magnet chuck or lifting device wherein a plurality of magnet elements are employed, with provision for arranging the elements in either aiding or in neutralizing relation.

A further object of the invention is to provide novel and effective actuating means for a permanent magnet chuck to accomplish the shifting between work-holding and work-releasing condition.

The several features of the invention will appear from the following description, taken in conjunction with the accompanying drawing in which:

FIG. l is a top plan view of a permanent magnet chuck constructed in accordance with the invention and embodying one form of actuating means for effecting the transisition between work-holding and work-releasing condition.

FIG. 2 is a sectional elevation of the chuck shown in ICC FIG. l and taken on the line 2 2 thereof, showing the parts in ON position for holding work.

FIG. 3 is a view taken in the same manner as FIG. 2, but with the parts shifted to release or OFF position.

FIG. 4 is a top plan view of a chuck having the magnet arrangement of FIG. 1 but embodying a modified construction for effecting the ON and OFF shifting operation.

FIG. 5 is a sectional View on the line 5 5 of FIG. 4 with the parts in flux-aiding or work-holding position.l

FIG. 6 is a view similar to FIG. 5 but with the chuck in OFF position.

FIG. 7 is a view in sectional elevation of another embodiment wherein the same general magnet arrangement is employed but with hydraulic operation of the elements.

The chuck illustrated in the several figures is of rectangular configuration and is provided with a plane top or work-holding surface. When used as a work lifting device, the apparatus would be utilized in inverted position, with the work-holding surface on the underside. Except for the magnet elements and their actuating means, .the principal structure of the chuck comprises a base 12 and a box-like top 14 having side and end Walls. The base and top should .be fabricated of a non-magnetic material sulch as stainless steel, aluminum alloy, or other suitable material of adequate strength.

The top, Work-holding face of the chuck, unlike prior known magnetic chucks, is malde up of an array of permanently magnetized elements 16, interposed with spacers 18 of soft iron or material of similar properties. The magnets 16 are in the form-of narrow strips extending preferably the (full width of the chuck top, and may be relatively deeper than their thickness.

As illustrated in the drawings, these magnets are magnetized across their narrow dimension to provide in each element N and S poles that lare relatively close together. It will further be observed that the magnet elle-ments are 'ar-ranged themselves with the polarity first one way and then the other. More specifically, the polarities of elements on each side of any one spacer are reversed, to wit: [N-S] [Sp-acer] [S-N] [Spacer] [N-S] and so on. Soft iron spacers are `also employed at each end of the magnet assembly, between the end magnet and the adjacent end portion of the top frame 14.

As has previously been indicated, the invention contemplates making use of certain improved magnetic materials that have recently become available. These mate,- -rials, ceramic or partly ceramic in nature, include the barium-iron oxide ceramic, also compositions of bismuth and manganese. These materials are notable for their high coercive force with good flux density, so that they may be effecively utilized when magnetized across the narrow dimension.

Being ceramic in nature, such magnet materials are not always suitable for exposure directly as part of the ltop work-holding surface of the chuck due to their somewhat brittle nature. Consequently it may in some instances be advantageous to recess the elements slightly below the plane of the adjacent iron spacers. In such case the recesses may be lled in with suitable non-magnetic material 19 of wear-resistant properties, such as stainless steel. A non-magnetic sintered tungsten carbide (nickelbonded) would also be suitable. If desired, a hard friction material or grit may be employed as or embedded in the filler material to increase the holding power of the chuck against sideways slipping of the work.

To enable the work to be released from the chuck when desired, and to provide maximum-,holding power in ON postion, the chuck employs airseco'nd array of magnet elements and soft iron spacerslnelow" the fixed array that forms the top surface of the chuck. The magnet elements 20 are of material similar to the fixed elements 16, but may be somewhat deeper, for a purpose hereinafter explained. With the parts as shown in FIG. 2, it will be observed that the polarities and order of alternating pole relationship for the movable array corresponds to the arrangement of the fixed array above. Thus it will =be seen that the magnets of the fixed and movable arrays are in aiding relation, equivalent to a single magnet extending the full depth of a stacked top and bottom magnet unit.

As a consequence of this relationship which is the ON or work-holding position, adjacent spacers are linked by very strong flux. In other words, considering the iron spacers 18 of FIG. 2, and running from left to right, the polarities are successively S-N-S-N etc. As a result, a

work piece need be only slightly wider than the width of a magnet element, or spacer, in order to span a fiux gap and consequently be effectively attracted. Of course, the larger the work piece, the more gaps are spanned, with consequent greater holding power.

It will be noted that the movable array shown in FIG. 2 includes at its left end an additional magnet element of N-S polarity. This element becomes effective when the movable array is positioned to turn the chuck off. Such OFF position is illustrated in FIG. 3 wherein it will be observed that the bottom array has been moved to the right a distance equal to the width of a magnet plus a spacer. In this position each magnet of the bottom array (including the left hand magnet that is inactive in FIG. 2) is in opposite-polarity relationship to the magnet directly above it of the top array. As a result, fluxlinking takes place vertically between upper and lower magnets through the spacers 18, Z2 on each side of a magnet pair, and little if any fiux remains available at the top surface. By making the magnets of the movable array somewhat deeper or wider than those of the top array, a balance can Ibe obtained wherein the neutralization of the fiux at the tops of the upper magnets may be made substantially complete in the OFF position of the movable array.

Actuation of the movable array of magnets and spacers may be carried out by means of a handle 28 on shaft 3i), with crank pin 32 on disc 34 serving to actuate link 36 pivotally connected to arm 3S secured in the soft iron end piece of the array. The crank throw is such as to shift the array the pitch distance between magnets upon 180 rotation of the handle. The array of magnets and soft iron spacers may be formed as a rigid structure by brazing the metal parts together and then cementing the magnets in place with a suitable resin, or by securing the parts by suitable non-magnetic clamping means or frame.

In FIGS. 4, and 6 a slightly modified actuating arrangement is employed for the movable array, the magnet structure being similar to that previously described. In this embodiment, clearance is provided between the underside of the movable array and the top surface of the base plate 12. A yoke 40 having arms 42 pivotally connected to non-magnetic side strips 44 secured toV and forming a part of the movable array is actuated by a crank and handle arrangement similar to that previously described.

The yoke arms 42 are tapered in shape, having a wide region substantially the width of the space between underside of the fixed array and the top surface of the base. As a consequence, rocking movement of the yoke, upon rotation of the crank and movement of the crank pin 46 upwardly, serves to move the movable array downwardly and away from the underside of the top array. Further rotation of the handle serves to effect the lateral displacement of the array, with the final movement rocking the yoke arms in reverse direction to raise the array into aligned contact with the xed array.

The advantage of this arrangement is to reduce the effort required to shift the movable array from OFF position. In this position, with unlike poles aligned, the arrays strongly attract each other, so that sliding movement is difiicult. By first prying the movable array downwardly and away from the fixed array, the lateral shift becomes substantially easier, and wear on the parts is greatly reduced.

At the other end of the stroke, where the arrays are to be in aiding relation for ON position, the arrays tend to repel one another unless there is a Work load on the chuck through which the major portion of the flux passes. Here the fulcruming of the yoke arms serves to raise the array into positive contact with the fixed array to insure maximum holding power. Set screws 50 permit adjustment of the yoke arms in ON position to bring about uniform contact between arrays. Springs could also be utilized to exert a force upwardly on the movable array.

As an alternative to direct mechanical operation of the movable magnet array, remote action by hydraulic means may readily be provided. FIG. 7 illustrates such a system in schematic fashion, wherein hydraulic fluid under pressure may be applied either to the left end or the right end of the movable array, by means of pump 60, four-way valve 62, and supply pipes 64, 66. By making the chuck so that the movable array substantially fills the region between base plate and top array, and between the sides of the movable array and the sides of the chuck body, the movable array may itself serve as the hydraulic piston and the chuck body the cylinder. Alternatively, a separate cylinder and piston might be employed.

While the invention has lbeen illustrated and described in terms of certain preferred and alternative embodiments, it will be understood that such embodiments are for purposes of illustration only, as examples of suitable arrangements utilizing a combination of fixed and movable arrays of relatively narrow magnets and spacers wherein the arrays may be disposed in aiding or in neutralizing relation to provide ON and OFF positions of the chuck. It will be further understood that the actuating mechanisms and arrangements for the movable array are merely illustrative, and other modes of effecting translation, with or without array separation during or coordinated with translation, are contemplated within the scope of the appended claims.

I claim as my invention:

1. A permanent magnet chuck comprising a pair of relatively-movable, adjacent, cooperating members, each of said members being an elongated member comprised of a plurality of plate-shaped permanent magnets and a plurality of plate-shaped soft magnetic bodies constituted of high permeability material abutting and interposed between each pair of adjacent magnets, said plate-.shaped magnets being magnetized in their thickness direction paralleling the length direction of the elongated members producing poles of like polarity on adjacent facing surfaces of each pair of magnets, means for displacing said members relative to one another over a distance of about the spacing between adjacent soft magnetic bodies, whereby in lone position poles of like polarity in the different members face one another producing a strong magnetic field at an external surface of the cooperatin-g members and whereby in another position poles of unlike polarity in the different members face one another to produce a very Weak magnetic field at said external surface, said permanent magnets in the member adjacent said external surface having a height dimension in a direction at right angles to the abutting surfaces of the members and the external surface significantly less than the corresponding height dimension of the magnets in the other member thereby to reduce the external magnetic field when said members occupy the said other position.

2. A controllable permanent magnet holding device comprising a casing, a plurality of permanent magnets and interposed flux-conductive spacer elements mounted in the casing in an array having an exposed work-contacting face, the magnets having major and minor axes parallel to the work-contacting face and being magnetized along their minor transverse axes, successive magnets from one end of the array to the other having alternately opposite polarities to present like poles of adjacent magnets on each side of a common spacer element, a second array of permanent magnets and interposed linx-conductive spacer elements, the transverse dimensions of magnets and spacers and the orientation of the magnetic axes of the magnets of the second array corresponding substantially to those of the first array, the second array being movably mounted within the casing and having a face adapted to contact the opposite face of the rst array from the work-contacting face, and means for moving the second array relative to the first array in the direction of the magnetic axes :of the magnets from a work-holding position in which the magnets of one array register in contact with magnets of the other array with like poles of registering pairs of magnets together, to a work-release position in which the magnets of the arrays substantially register and contact with one another with both poles of the magnets of one array in unlike pole relationship tro both poles ofthe registering magnets of the other array, the magnets of the movable array being dimensionally larger in a direction perpendicular to the workcontacting face of the device than the magnets of the xed array.

3. A controllable permanent magnet holding device comprising a casing, a plurality of permanent magnets and interposed flux-conductive spacer elements mounted in the casing in an array having an exposed work-contacting face, the magnets having major and minor axes parallel yto the work-contacting face and being magnetized along their minor transverse axes, successive magnets from one end of the array to the other having alternately opposite polarities to present like poles of adjacent magnets on each side of a common spacer element, a second array of permanent magnets and interposed flux-conductive spacer elements, the transverse dimensions of magnets and spacers and the orientation of the magnetic axes of the magnets of the second array corresponding substantially to those of the lirst array, the second array being movably mounted within the casing and having a face adapted -to contact the opposite face of the irst array from the Work-contacting face, and means for moving the second array relative to the rst array in the direction of the magnetic axes of the magnets from a work-holding position in which the magnets of one array register in contact with magnets of the other array With like poles of registering pairs of magnets together, to a work-release position in which the magnets of the arrays substantially register and contact with one another with both poles of the magnets of one array in unlike pole relationship to both poles of the registering magnets of the other array, said means for moving the second array relative to the rst array including mechanism for separating the arrays at the commencement of the shifting :of the movable array out of registration with the xed array.

4. A holding device according to claim 3 having means for moving the movable array into contact with the xed array against the force of magnetic repulsion upon moving the movable array into work-holding registration.

5. A holding device according to claim 3 having means including a camming lever for positioning the movable array in contact with `the xed array when the arrays are substantially in work-releasing and work-holding registration and for supporting the movable array in separated relation when the latter is in positions intermediate registering relation.

6. A holding device according to claim 3 in which the means for shifting the movable array comprises a rock shaft journalled in the casing, an external handle for operating the rock shaft, and connections between the movable array and the rock shaft comprising a link pivotally connected at one end to the array and at the other end to the rock shaft in eccentric relation to the rock shaft axis, said link having a cam surface to pry the movable array away from the fixed array upon rocking movement of the' rock shaft.

7. A holding device according to claim 3 in which the means for shifting the movable array comprises a rock shaft journalled in the casing, an external handle for operating the rock shaft, and connections between the movable array and the rock shaft comprising a yoke having spaced arms pivotally connected to the movable array :on opposite sides thereof, the other end of the yoke being pivotally connected to the rock shaft in eccentric relation to the axis thereof, the yoke arms having cam surfaces adjacent the connections to the movable array for prying the movable array from the fixed array upon rocking movement of the rock shaft.

References Cited bythe Examiner UNITED STATES PATENTS JOHN F. BURNS, Primary Examiner.

SAMUEL BERNSTEIN, Examiner. 

1. A PERMANENT MAGNET CHUCK COMPRISING A PAIR OF RELATIVELY-MOVABLE, ADJACENT, COOPERATING MEMERS, EACH OF SAID MEMBERS BEING AN ELONGATED MEMBER COMPRISED OF A PLURALITY OF PLATE-SHAPED PERMANENT MAGNETS AND A PLURALITY OF PLATE-SHAPED SOFT MAGNETIC BODIES CONSTITUTED OF HIGH PERMEABILITY MATERIAL ABUTTING AND INTERPOSED BETWEEN EACH PAIR OF ADJACENT MAGNETS, SAID PLATE-SHAPED MAGNETS BEING MAGNETIZED IN THEIR THICKNESS DIRECTION PARALLELING THE LENGTH DIRECTION OF THE ELONGATED MEMBERS PRODUCING POLES OF LIKE POLARITY ON ADJACENT FACING SURFACES OF EACH PAIR OF MAGNETS, MEANS FOR DISPLACING SAID MEMBERS RELATIVE TO ONE ANOTHER OVER A DISTANCE OF ABOUT THE SPACING BETWEEN ADJACNET SOFT MAGNETIC BODIES, WHEREBY IN ONE POSITION POLES OF LIKE POLARITY IN THE DIFFERENT MEMBERS FACE ONE ANOTHER PRODUCING A STRONG MAGNETIC FIELD AT AN EXTERNAL SURFACE OF THE COOPERATING MEMBERS AND WHEREBY IN ANOTHER POSITION POLES OF UNLIKE POLARITY IN THE DIFFERENT MEMBERS FACE ONE ANOTHER TO PRODUCE A VERY WEAK MAGNETIC FIELD AT SAID EXTERNAL SURFACE, SAID PERMANENT MAGNETS IN THE MEMBER ADJACNET SAID EXTERNAL SURFACE HAVING A HEIGHT DIMENSION IN A DIRECTION AT RIGHT 